The invention relates generally to both methods of refining crude vegetable oils and crude animal fats, as well as, cavitation apparatuses that are used for processing fluidic mixtures. The invention uses energy released upon implosion and/or pulsation of cavitation features to alter properties of the fluids. More particularly, the present invention relates to the degumming of oils by utilizing cavitational processing to modify hydratable and/or non-hydratable phosphatides (NHP) and metals followed by separation to obtain a refined and more valuable product. The method finds applications in food, chemical, pharmaceutical and other industries.
The preferred oils that can be refined and/or degummed using the present invention are edible vegetable oils, i.e., canola, coconut, corn, cottonseed, grape seed, ground nut, linseed, palm, peanut, rapeseed, rice bran, safflower, soybean, sunflower and other edible vegetable oils that are valuable food sources. Crude vegetable oils can be produced from vegetable seeds by solvent extraction followed by filtration of the obtained miscella to remove solids and particulate.
Crude vegetable oils are comprised mainly of triglycerides and contain impurities, such as phosphatides, free fatty acids (FFA), off-flavor compounds, chlorophyll and other pigments, waxes, and metals, such as aluminum, calcium, copper, iron, magnesium and potassium. The impurities negatively affect taste, smell, appearance and shelf life of oils and, thus, have to be removed before consumption.
The crude oils are produced by pressing flaked (comminuted), dried seeds or beans. The cold-pressed oil is obtained from seeds without prior heating. The oilseeds may be hot-pressed following conditioning at ˜80° C. for about a half an hour. Hot pressing provides better yields but can lead to increased oil deterioration and accumulation of non-hydratable phosphatides, i.e. calcium, iron and magnesium salts of phosphatic acid and phosphatidylethanolamine (PE) due to the action of lipases and other enzymes that are highly active at 57-85° C.
Phosphatides are derivatives of glycerol phosphate, which normally contain a nitrogenous base. Phosphatic acid has a glycerol backbone with a saturated fatty acid bonded to carbon 1, an unsaturated one attached to carbon 2, and a phosphate group bonded to carbon 3. Elevated levels of PA are found in unripe, damaged, sick and over moist seeds. To assure a higher quality of oil, commercial producers minimize the exposure of seeds to temperatures in the 57-80° C. range during storage, treatment and transportation. In order to deactivate phosphalipases, seeds are treated with steam heated to 150-170° C. After such treatment, the concentrations of iron, calcium and magnesium salts of phosphatic acid reduce to ˜25-50% of the amount obtained through conventional processing (Cmolik and Pokorny, 2000; Gunstone etal., 2007).
When producing biodiesel from such crude oils, it is highly desirable to reduce the phosphorus content to at most 20 ppm in oil, grease, fat or tallow feedstock to ensure that the final product meets EPA regulatory standards on diesel engine exhaust emission. Oil refining procedures depend on the type of oil and its composition and usually consist of degumming, alkali neutralization, bleaching and deodorization. Degumming refers to the removal of phosphatides and other similar compounds by adding water and/or acid to oil and centrifuging. The main purpose of the degumming is to remove phosphorus, which is present in the crude oil in the form of hydratable phosphatides and NHP. Without efficient removal of the phosphatides, the downstream refining procedures may not deliver acceptable results. In addition to the removal of NHP, the removal of iron and other metals is highly desirable (Racicot and Handel, 1982; Cvengros, 1995; Cmolik and Pokorny, 2000). The oil then can be bleached, dewax, hydrogenated and/or deodorized to produce a more stable product.
A number of prior art degumming methods have been developed, including water degumming (treatment of crude oil with hot water); acid degumming (treatment of crude oil with phosphoric acid or citric acid); acid refining (treatment of water-degummed oil with an acid, which is then partially neutralized with alkali and centrifuged to remove residual gums and free fatty acids); dry degumming (acid degumming with very small amount of water, combined with bleaching); enzymatic degumming (modification of phospholipids with enzymes to obtain the water-soluble compounds); degumming with help of chelating agents (EDTA-ethylenediaminetetraacetic acid, aspartic amino acid, organic malic and fumaric acids, etc.); and membrane/ultra filtration degumming (passage of crude oil through a semi permeable membrane impermeable to phospholipids).
Physical refining, also known as dry or steam refining, is based on the higher volatility of FFA compared to triglycerides. In this method, removal of FFA via neutralization is substituted by simultaneous deacidification-deodorization. The techniques of degumming, alkaline refining, bleaching, hydrogenating, dewaxing and deodorizing are well known in the art. It should be understood that each refining procedure results in some loss of oil.
Phospholipids are the major constituents of biological membranes, which are present in all living species. They are quantified by determining the phosphorus (P) content, i.e., the total concentration of phospholipids in oil is indicated as parts per million of phosphorus (ppm P). The concentration of phospholipids is calculated by multiplying the measured value for ppm P by a factor 30. For example, the phosphorus content of crude soybean oil is 400-1200 ppm and that of the degummed oil is usually 10-100 ppm. The phosphatide content of the oil should be close to 20 ppm P before bleaching and 5 ppm P before stripping.
If the key objective of degumming is the removal of hydratable phospholipids, the preferred procedure is water degumming. In this method, warm crude oil is usually treated with superheated steam (220° C. or higher) under low pressure. Hydratable phosphatides become insoluble in oil due to the absorption of water and, therefore, can be efficiently isolated. A gum layer that forms after a period of time is separated via centrifuging and is used for production of lecithin.
Lecithin is recognized by the FDA as GRAS, i.e. Generally Regarded as Safe, 21 CFR, 1841400, and is used as a non-toxic surfactant, emulsifier, lubricant and to produce liposomes. Commercial lecithin is a mixture of various phospholipids, such as phosphatic acid, phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol, depending on the source and production. In hydrolyzed lecithin, one fatty acid is removed by a phospholipase.
Water degumming is utilized commonly with palm and coconut oils and is not associated with significant oil loss, saponification, or environmental pollution. However, the water-degummed oils may contain 100-250 ppm P in the form of NHP, resulting in poor quality and low oxidative stability (Racicot and Handel, 1982; Athenstaedt and Daum, 1999). In this case, water-degumming is typically followed by or substituted with acid degumming or another procedure.
Degumming of crude triglyceride oils that were not affected by a prior enzymatic activity is disclosed in U.S. Pat. No. 5,696,278 to Segers. The process in Segers involves repeated and prolonged heating of the oil.
Soybean, sunflower and many other oils are usually acid degummed due to a high level of calcium and magnesium salts of phosphatic acid, which cannot be removed by water degumming. In acid degumming, phosphoric acid, citric acid, oxalic acid, tartaric acid or maleic anhydride are dispersed in oil followed by raising the pH with a base, and separating the NHP, FFA, liposaccharides, lipoproteins and some trapped triglycerides. The acid degumming requires downstream washing and can be associated with a substantial oil loss. The acid-degummed oil then is decolorized by heating in the presence of bleaching earth, charcoal or attapulgite clay at a reduced pressure (Lin and Yoo, 2007). In a final deodorization step, volatile compounds are removed from the bleached oil by steam stripping under vacuum. In practice, the numerous combinations of these and other procedures are applied, depending on certain properties of the oils. For example, the concentration of phospholipids in the oil can be lowered to 5 ppm P by using EDTA and emulsifying additives following the extraction of phospholipids with hot water (Choukri et al., 2001).
U.S. Pat. No. 4,698,185 to Dijkstra etal. discloses a process for the simultaneous production of degummed vegetable oils and gums with a high PA concentration. The starting materials for this process are water-degummed vegetable oils, which contain excessive NHP and iron. In a first stage, phosphoric acid is dispersed in the water-degummed oil and sufficient time is allowed for the salts of phosphatic acid to decompose. In a second stage, a base is added to increase the pH value above 2.5 without causing substantial saponification. In a third stage, the aqueous phase containing the gums and the oil phase are separated. While this process results in degummed oil with very low phosphorus and iron concentrations and gums of high PA content with improved usability, it requires multiple processing steps and a prolonged residence time.
Triglyceride oils can be degummed by using alkali. The method comprises the conversion of FFA in soaps and the separation of phospholipids that concentrate in the water phase. However, the alkali degumming requires oil washing and extra centrifugations and produces waste in the form of soap. Acid degumming is a preferred process.
Another degumming procedure allows for the removal of NHP from oils by using potassium and sodium chloride. The water-degummed soybean, rice bran and mustard oils treated with the solution of 1.5% potassium chloride and 0.5% sodium chloride (95:5 v/v), contains as low as 0.05, 0.06 and 0.02% phospholipids, correspondingly. This method, when combined with water degumming, removes NHP with ˜4% oil loss (Nasirullah, 2005).
Phospholipases, the enzymes that modify phospholipids, have found numerous applications in oil degumming, which has resulted in substantial environmental benefits. The efficiency of enzymatic degumming is improved via genetic engineering (De Maria etal., 2007).
Among the methods of physical degumming, the application of selective membranes is a promising method that offers several advantages over conventional technologies. Ultrafiltration efficiently separates phospholipids and can be utilized in both degumming and dewaxing of undiluted oils and oils diluted with hexane to improve flux. Nonporous membranes are a better choice for simultaneous degumming, dewaxing and decolorization. Further improvement of membrane technology is desirable for industrial application (Manjula and Subramanian, 2006).
It is well known that an increase in both pressure and temperature along with vigorous mixing provided by cavitation can initiate and accelerate numerous reactions and processes. Enhancing the reaction yields and process efficiencies by means of the energy released upon the collapse of cavities generated in the fluidic media has found numerous applications. Although extreme pressure or heat can be disadvantageous, the outcome of an optimized cavitation treatment has proven to be beneficial.
Cavitation can be of different origins, including hydrodynamic, acoustic, ultrasonic, laser-induced and generated by injecting steam into a cooled fluid. Simultaneous application of two or more cavitation-generating techniques may provide an even better outcome, i.e., coupling steam injection cavitation with acoustic cavitation improves efficiency by 16 times (Young, 1999; Gogate, 2008; Mahulkar etal., 2008).
It has been reported that crude soybean oil can be quickly degummed by applying ultrasound sonication in the presence of a small amount of degumming agent (Moulton and Mounts, 1999). The procedure removes up to 90-99% phospholipids. However, it should be noted that the sound technology requires using a batch environment. Since the effect diminishes with the increase in a distance from the radiation source, the treatment efficacy of sonic cavitation depends on a container's size and is low with larger vessels. The alterations occur at particular locations, depending on the radiation frequency and, thus, are not uniform. Moreover, sound-assisted cavitation cannot be used efficiently in continuous processes with a high throughput. In sonic cavitation, the energy requirement is too high and the residence time is too long to be economically feasible for high throughput degumming. The power requirements for ultrasonic devices integrated in-line may reach 1 MW for 20-100 m3/h flow velocities.
Distinct from acoustic cavitation, flow-through hydrodynamic cavitation does not require using a vessel. Numerous flow-through hydrodynamic apparatuses are known. See, for example, U.S. Pat. No. 6,705,396 to lvannikov etal. and U.S. Pat. Nos. 7,338,551, 7,207,712, 6502,979, 5,971,601 and 5,969,207 to Kozyuk that disclose hydrodynamic cavitation apparatuses and their applications.
Now, with the cost of energy and human health concerns rising rapidly, it is highly desirable to lower level of impurities in edible oils and biodiesel and reduce the energy consumption of refining. The prior art techniques do not offer the most efficient method of degumming and refining of oils, especially edible vegetable oils in the shortest amount of time possible.
Therefore, a need exists for an improved method for processing oils and fats. The inventive method and devices are desired particularly at oil refineries during harvest, when throughput is a key factor. The present invention provides such methods and devices, while producing improved product with shorter processing time and less accumulation of waste harmful to environment.
The present invention provides a method and device for generating cavitation in a flow of oil to be treated within at least one cavitation chamber, preferably in multiple consecutive cavitation chambers. This goal is achieved through the design of a cavitation device aimed at fast degumming/refining of vegetable oils and animal fats.
To achieve as large a profit margin as possible it is necessary to decrease time, energy consumption and eliminate waste production of degumming. The prior art methods do not offer the most efficient method in the shortest time possible. Therefore, a need exists for the improved method and device for oil degumming with a minimal residence time and energy cost that produces degummed oils with low levels of phosphorus and metals. The present invention satisfies these needs and provides other related advantages.